In all electrical motors containing commutator and brushes, the contact between commutator and conductive brushes, is a source of sparking. If such motor operates in environment containing flammable gases, it might lead to a fire or even to an explosion.
Well known solutions to prevent explosion are totally sealed motors. First disadvantage of such solution is poor dissipation of heat. Consequentially, for same output power, a larger and more expensive motor is needed. Second disadvantage is the brush dust which remains inside the motor. Brush dust is conductive and could be a reason for leakage current. Brush dust can be a also reason for premature bearing failure.
Another solution to prevent the explosion is described in U.S. Pat. No. 6,417,595 B1 applied by McMillan Electric Company. Main elements which provide protection are the collar embracing commutator, the seal on one said of the commutator and the labyrinth on the other side of the commutator. This solution is more cost effective as totally sealed motor.